1. Field of the Invention
The invention relates to a method of producing a semiconductor laser device.
2. Description of the Related Art
In general, for a semiconductor laser chip (hereinafter, referred to merely as "laser chip") 1, as shown in FIG. 4, a current of a predetermined level is injected into the active layer inside the laser chip 1 via electrodes 2 formed on the front and back surfaces of the laser chip, so that laser light 4 is oscillated through light emitting end surfaces 3 formed on the both ends of the laser chip 1 by a cleavage process. In order to protect the light emitting end surfaces 3 and adjust the reflectivities of the light emitting end surfaces 3 for realizing the laser oscillation, coating films 5 which are made of alumina (Al.sub.2 O.sub.3), silicon oxide (SiO.sub.2), silicon nitride (SIN), or the like are formed on the laser chip 1.
As a method of forming the coating films 5 on the laser chip 1, conventionally, known is a method shown in FIGS. 5(a) and 5(b). As shown in FIG. 5(a), electrodes 2 are disposed on a wafer in which several tens to several hundreds of laser elements are formed, and the wafer is then cleft so as to form laser bars 6 in which a plurality of laser elements are laterally aligned in a line. As shown in FIG. 5(b), thereafter, the laser bars 6 are fixed to a support platform 9 under the state where they are arranged by using alignment jigs 7 in such a manner that the light emitting end surfaces 3 are positioned at the upper and lower sides, and the ends of the laser element group are clamped and held by fixing jigs 8. A process of sputtering or evaporation is then performed from the above to form the coating film 5 on each of the light emitting end surfaces 3 of each laser bar 6.
After the formation of the coating films 5, each laser bar 6 is split into separate laser chips 1. Each laser chip 1 is fixed to a submount 10 by soldering or the like, as shown in FIG. 6. The submount 10 on which the laser chip 1 is mounted is fixed to a heat sink 22 projecting upward from a stem 21. The electrode on the upper surface of the laser chip 1 is electrically connected to the submount 10 by a wire 24a. Similarly, a surface electrode of the submount 10 is electrically connected to a terminal pin 23b by a wire 24b. A photodiode 27 is disposed in order to monitor laser light emitted from the laser chip 1, and the electrode of the photodiode 27 is electrically connected to a terminal pin 23c by a wire 24c. Finally, the stem 21 is sealed by a cap 26 having a glass plate 25, thereby completing a laser unit 20.
However, the conventional method of forming the coating films 5 has the following problems. When the laser bars 6 are clamped by the alignment jigs 7, the light emitting end surfaces 3 may project from the alignment jigs 7 by a larger distance. In such a case, the coating films 5 are elongated so as to be formed also on the electrodes 2, resulting in that the heat radiation property of the laser chip 1 is impaired, and that the process of fixing the laser chip onto the submount 10 and the wire bonding process are obstructed. In the case where the light emitting end surfaces 3 project from the alignment jigs 7 by a smaller distance, conversely, there arises another problem in that the resulting coating films 5 cannot have a sufficient thickness.
Compound semiconductor materials constituting such a laser element are softer than usual semiconductor materials containing Si. Therefore, the clamping pressure exerted by the fixing jigs 8 cannot be increased to a value higher than a given level. As a result, gaps are formed between the laser bars 6 and the alignment jigs 7. The coating films reach the electrodes 2 through the gaps to be formed thereon, thereby raising the same problem as that discussed above.
Since the laser bars 6 have a very small width, they must be handled with extra care. This raises a further problem in that mass production of such laser devices requires much labor.